Emission controlled current limiter for use in electric power transmission and distribution

Abstract

Method and apparatus are provided for an emission controlled current limiting device. The apparatus may control the current thermionically, by cold cathode emission, by photo-emission, or with plasma devices; the common feature being that the current is limited by controlling a series emission process. The apparatus has applications in both power line transmission and distribution networks to protect existing utility equipment and reduce the cost of new equipment.

What is claimed is: 
     
       1. For use in limiting fault currents in electrical power transmission and distribution lines, a fault current limiting circuit comprising a first emission limited device having a cathode element, an anode element, and means for effecting the emission of current carriers from said cathode whereby current carrier emission is limited above the current level established by said means for effecting the emission; a second emission limited device having a cathode element, an anode element, and means for effecting the emission of current carriers from said cathode whereby current carrier emission is limited above the current level established by said means for effecting the emission; and means connecting said first emission limited device and said second emission limited device in parallel and in opposite polarity. 
     
     
       2. A fault current limiting circuit as defined by claim 1 and further including low impedance switch means, means connecting said switch means in parallel with said first and second current limited device, and means responsive to a current in said electrical power line for maintaining said switch means closed in response to normal operating current levels, and for opening said switch means in response to a fault current. 
     
     
       3. A fault current limiting circuit as defined by claim 2 wherein said means for limiting current comprises means for heating said cathode whereby current carrier emission is limited thermionically. 
     
     
       4. A fault current limiting circuit as defined by claim 3 wherein said cathode comprises a surface layer of material which ionizes at a rate that is determined by the volume and surface area of the material and electron emission rate. 
     
     
       5. A fault current limiting circuit as defined by claim 3 wherein said cathode is cylindrical and said anode is cylindrical and coaxial with said cathode. 
     
     
       6. For use in limiting fault currents in electrical power transmission and distribution lines, an emission limited device comprising a cathode element, an anode element, and means for effecting the emission of current carriers from said cathode whereby current carrier emission is limited above the current level established by said means for effecting the emission, said cathode comprising a surface layer of material which ionizes at a rate that decreases above a level determined by the volume and surface area of said material, and said anode and said cathode are separated by a varying gap distance. 
     
     
       7. An emission limited device as defined by claim 6 wherein said means for effecting emission of current carriers includes a grid electrode. 
     
     
       8. An emission limited device as defined by claim 6 wherein at least one element is segmented. 
     
     
       9. For use in limiting fault currents in electrical power transmission and distribution lines, an emission limited device comprising a cathode element, an anode element, and means for effecting the emission of current carriers from said cathode whereby current carrier emission is limited above the current level established by said means for effecting the emission, said cathode comprising a surface layer of material which ionizes at a rate that decreases above a level determined by the volume and surface area of said material, and at least one element is segmented. 
     
     
       10. An emission limited device as defined by claim 9 wherein said means for effecting emission of current carriers includes a grid electrode.